title: Transmural atrial fibrosis after epicardial and endocardial argon-powered CryoMaze ablation.
abstract: BACKGROUND
  The CryoMaze procedure is usually limited to endocardial ablation under cardio-pulmonary bypass. Epicardial ablation is considered inferior as endocardial islets of atrial tissue could theoretically remain viable, protected from cryoinjury by epicardial fat and endocardial circulating warm blood. Novel argon-powered cryoprobes with lower ablation temperatures have recently become available. It is unclear if these instruments can reliably induce transmural atrial fibrosis by epicardial cryoablation on the beating heart.
  
  
  METHODS
  Ten sheep were divided into two equal groups. CryoMaze ablations were applied using an argon-powered cryoprobe with an ablation temperature of -185°C. In the control group, standardized ablations (n = 50) were applied endocardially under cardiopulmonary bypass. In the experimental group, corresponding ablations (n = 50) were applied epicardially on the beating heart. Postoperatively the animals were monitored for 30 days. At necropsy, the lesions were explanted and analyzed histologically for evidence of transmural fibrosis.
  
  
  RESULTS
  Two animals in the control group and one animal in the experimental group died prematurely. Autopsy of the remaining animals showed that all lesions (n = 70) had retained their structural integrity. In the control group, histology demonstrated transmural fibrosis in 94% (28/30) of the endocardially applied lesions. In the experimental group, histology demonstrated transmural fibrosis in 95% (38/40) of the epicardially applied lesions. Statistical analysis revealed no significant difference between the two groups (p = 0.96).
  
  
  CONCLUSIONS
  Argon-powered epicardial cryoablation on the beating heart is as efficient in inducing transmural fibrosis as the traditional technique of endocardial ablation under cardio-pulmonary bypass.
authors.affiliation: Experimental Surgical Services, University of Minnesota, Minneapolis, Minnesota, USA. rgallegos@partners.org
authors.forename: Robert P
authors.initials: RP
authors.lastname: Gallegos
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Rivard
authors.forename: Taufiek K
authors.initials: TK
authors.lastname: Rajab
authors.forename: B
authors.initials: B
authors.lastname: Chir
authors.forename: Jan D
authors.initials: JD
authors.lastname: Schmitto
authors.forename: Matthew T
authors.initials: MT
authors.lastname: Lahti
authors.forename: Nicole
authors.initials: N
authors.lastname: Kirchhof
authors.forename: Richard W
authors.initials: RW
authors.lastname: Bianco
mesh_terms: D000818:Animals; D001281:Atrial Fibrillation / Q000601:surgery*; D004195:Disease Models, Animal; D004699:Endocardium / Q000601:surgery*; D005355:Fibrosis / Q000209:etiology / Q000473:pathology; D006325:Heart Atria / Q000473:pathology*; D053685:Laser Therapy / Q000009:adverse effects* / Q000295:instrumentation; D054018:Lasers, Excimer / Q000009:adverse effects / Q000627:therapeutic use*; D009206:Myocardium / Q000473:pathology*; D011183:Postoperative Complications; D011667:Pulmonary Veins / Q000601:surgery; D012756:Sheep